The present invention relates to a projection display apparatus.
FIG. 12 shows a typical relationship between illuminance of a projected image and a level of an input signal (achromatic color) in a projection display apparatus used in a dark room isolated from the ambient light. In this figure, ILx denotes illuminance of apart of a screen at black level (achromatic color, input signal level: zero). Even when a signal input to the projection display apparatus is at a zero level, ILx does not become zero, since an LCD panel used as a light valve in the projection display apparatus cannot block the light completely.
When the projection display apparatus is used not in a dark room but in an environment where the ambient light falls on the screen (when the room is lit so that viewers can take notes in a presentation, for example), illuminance ILy of the screen due to the ambient light disables parts of the screen at levels which are below ILy and close to a black level from being reproduced (referred to as xe2x80x9cblack-level subsidencexe2x80x9d hereinafter), thereby narrowing a dynamic range as shown in FIG. 13. On the other hand, when the projection display apparatus is used in a dark environment where illuminance ILz of the screen due to the ambient light is lower than ILx, a black level is undesirably higher than ILz by ILxxe2x88x92ILz (referred to as xe2x80x9cblack-level risexe2x80x9d hereinafter)
Furthermore, when a color-reproducible range of a projected image in a dark room isolated from the ambient light is as shown by a crosshatched portion of FIG. 15 which represents an x-y chromaticity diagram of the CIE XYZ color system, if white ambient light is applied to the projected image, the color-reproducible range is narrowed as shown in FIG. 16. When tinted light is used instead of white light for lighting, not only the color-reproducible range is narrowed, but also its shape is changed.
Generally, the projection display apparatus is provided with facilities of brightness adjustment and contrast adjustment, so that the user can adjust brightness and contrast viewing an image projected onto the screen. However, these facilities cannot fully accommodate the above-described black-level rise, black-level subsidence, narrowing of the dynamic range and deterioration of color-reproduction characteristic. Besides, since adjustment of brightness or contrast is achieved by arithmetic operation on video signals which are generally converted into digital signals, when a digital video signal is formed from 8 bits, unless the bit length is extended sufficiently during the arithmetic operation temporarily, to 10 bits for instance, the dynamic range can be narrowed due to accumulation of calculation errors. This accumulation of calculation errors can also cause the projected image to exhibit false contours.
The present invention has been made to solve the above-described problems with an object of improving the black-level reproduction characteristic, the dynamic range, and the color reproduction characteristic of an projected image.
The above-described object of the invention can be achieved by a projection display apparatus in which a light emitted from a light source enters a light valve, an image corresponding to an input video signal is formed in an image-forming plane of the light valve, and the formed image is projected onto a screen through an optical system, the projection display apparatus comprising:
a first processor for calculating an area of an image projected onto the screen;
a photometer for measuring illuminance in the neighborhood of the image projected onto the screen;
a second processor for calculating a black-level correction value from the area of the image calculated by the first processor and the illuminance measured by the photometer; and
a light-source-power controller for controlling power supplied to the light source on the basis of the black-level correction value calculated by the second processor.
The projection display apparatus may further comprise a distance-measuring device for automatically measuring a distance between the projection display apparatus and the screen, the first processor automatically calculating the area of the image projected onto the screen on the basis of a target position of a zoomlens included in a projection lens unit of the optical system and the distance measured by the distance-measuring device.
The projection display apparatus may further comprise a first timer which is reset when the power supplied to the light source is changed by the light-source-power controller and starts to measure a time elapsed after reset of the first timer, the light-source-power controller keeping the power supplied to the light source constant until a count value of the first timer reaches a predetermined value.
The projection display apparatus may further comprise a first memory which samples the illuminance measured by the photometer at regular time intervals and stores resultant samples in succession, and a third processor for calculating an average of the samples stored in the first memory, the second processor calculating the black-level correction value on the basis of the average of the samples supplied from the third processor.
The light-source-power controller may keep the power supplied to the light source constant irrespective of the illuminance measured by the photometer until a predetermined time elapses after light up of the light source.
The projection display apparatus may further comprise a fourth processor which, when the illuminance in the neighborhood of the projected image measured by the photometer is higher than a maximum black level obtainable through control by the light-source-power controller, corrects an input video signal in order to adjust brightness and contrast of the projected image by a value corresponding to a difference between the illuminance in the neighborhood of the projected image and the maximum black level.
The light source may include a discharge tube whose tube voltage varies with increase of a cumulative lighting time thereof, and the projection display apparatus may further comprise a second timer for measuring the cumulative lighting time of the light source, and a second memory storing a characteristic of variation of the tube voltage with the increase of the cumulative lighting time of the light source, the light-source-power controller compensating for variation of the power supplied to the light source due to the variation of the tube voltage on the basis of the cumulative lighting time supplied from the second timer and the characteristic of the variation of the tube voltage supplied from the second memory.
The above-described object of the invention can be also achieved by a projection display apparatus in which a light emitted from a light source enters a light valve, an image corresponding to an input video signal is formed in an image-forming plane of the light valve, and the formed image is projected onto a screen through an optical system, the projection display apparatus comprising:
a light-source-power controller for controlling power supplied to the light source on the basis of a black-level correction value supplied from outside;
a signal generator for generating a testing video signal used for projecting a test image including a plurality of regions disposed in order of brightness; and
an adjuster allowing adjustment to the black-level correction value supplied to the light source with the test image being projected onto the screen.